As the biotechnology has been developed, a flow cytometer is more commonly used in the fields of medicine and biology for automatic analysis and fractionation of cells or chromosomes (which are collectively referred to as “cells”). The flow cytometer forms a stream of the analyte cells within a flow channel performing as cell aligning means, and irradiates laser beam on the stream of the cells to detect information light scattered/emitted at the cells (i.e., forward- and side-scattered light, and fluorescent light). Also, it converts the information light into electrical signals to analyze the cells based upon the electrical signals, allowing high throughput of analyzed cells and extraction (sorting) of a particular group of cells, if necessary.
FIG. 16 is a schematic view of the flow cytometer, for illustrating a typical structure and operation thereof. In the flow cytometer 200 shown in the drawing, a liquid suspension 201 containing cells received in a container and a sheath fluid 202 received in another container are each guided into a funnel-shaped flow chamber (nozzle) 204 by air pumps 203. Within the flow chamber 204, the sheath fluid 202 forms a cylindrical laminar flow, i.e., a sheath flow, encompassing the liquid suspension 201 therein, in which a discrete one of the cells runs one-by-one along the central axis of the flow chamber 204. As closer to the bottom end of the flow chamber 204, the sheath flow runs faster, in which a laser beam 207 is irradiated from a laser beam source 205 and focused by a collective lens 206. Most of the cells in the liquid suspension 201 are fluorescently labeled with fluorescent material such as a fluorescent pigment and a fluorescent-labeled monoclonal antibody. Therefore, irradiation of the laser beam onto the cells generates the scattered light and the fluorescent light.
The scattered light passes through collective optics including a collective lens 208 and a beam block 209 to an optical detector 210 such as a photodiode designed for detecting the scattered light. In the meanwhile, a red-based fluorescent light is received by means of an optical detector 215, through another collective optics including a collective lens 211, a half-mirror 212, a collective lens 213 and a filter 214, also a green-based fluorescent light is received by means of an optical detector 218, through the half-mirror 212, a collective lens 216 and a filter 217. Photomultiplier tubes are typically utilized as the fluorescent detectors 215, 218 capable of detecting faint fluorescent light. A signal processing circuitry 219 receives various signals output from the detector 210 for the scattered light, the detector 215 for the red-based fluorescent light and the detector 218 for the green-based fluorescent light, and analyzes strength of the scattered light and the fluorescent lights, thereby to identify the analyte cell.
As illustrated in FIG. 17, the identification result is transmitted from the signal processing circuitry 219 to an electron charger 220. The electron charger 220 charges the liquid suspension 201 and the sheath fluid 202 with electrons of a predetermined polarity in accordance with the identification result of the cells, just before the identified cell reaches the break-off point 221 at the bottom end of the sheath flow and a droplet containing the identified cell is formed, i.e., just before the identified cell reaches break-off point at the bottom end of the sheath flow to be the droplet. As the result, the droplet split off the sheath flow at the break-off point 221 is charged with the electrons of the predetermined polarity. The charged droplet falling downwardly is attracted and deflected between a pair of electrodes 222, 223 which are provided beneath the break-off point 221 and applied with potential of different polarity, so that the droplet is sorted into one of the collection tubes 224, 225 which are arranged below the electrodes 222, 223. (See, for example, Patent References 1-4.)
Patent Reference 1: JP 59-000643, A
Patent Reference 2: JP 59-184862, A
Patent Reference 3: JP 60-195436, A
Patent Reference 4: JP 03-503808, A